1. Field of the Invention
In one of its aspects, the present invention relates to an optical radiation sensor system. In another of its aspects, the present invention relates to a method for measuring radiation transmittance of a fluid.
2. Description of the Prior Art
Optical radiation sensors are known and find widespread use in a number of applications. One of the principal applications of optical radiation sensors is in the field of ultraviolet radiation fluid disinfection systems.
It is known that the irradiation of water with ultraviolet light will disinfect the water by inactivation of microorganisms in the water, provided the irradiance and exposure duration are above a minimum xe2x80x9cdosexe2x80x9d level (often measured in units of milliWatt seconds per square centimeter or mWxc2x7s/cm2). Ultraviolet water disinfection units such as those commercially available from Trojan Technologies Inc. under the tradenames Trojan UVMax(trademark), Trojan UVSwift(trademark) and Trojan UVLogic(trademark), employ this principle to disinfect water for human consumption. Generally, water to be disinfected passes through a pressurized stainless steel cylinder which is flooded with ultraviolet radiation. Large scale municipal waste water treatment equipment such as that commercially available from Trojan Technologies Inc. under the tradenames UV3000 and UV4000, employ the same principal to disinfect waste water. Generally, the practical applications of these treatment systems relates to submersion of a treatment module or system in an open channel wherein the wastewater is exposed to radiation as it flows past the lamps. For further discussion of fluid disinfection systems employing ultraviolet radiation, see any one of the following:
U.S. Pat. No. 4,482,809,
U.S. Pat. No. 4,872,980,
U.S. Pat. No. 5,006,244,
U.S. Pat. No. 5,418,370,
U.S. Pat. No. 5,539,210, and
U.S. Pat. No. Re36,896.
In many applications, it is desirable to monitor the level of ultraviolet radiation present within the water (or other fluid) under treatment or other investigation. In this way, it is possible to assess, on a continuous or semi-continuous basis, the level of ultraviolet radiation, and thus the overall effectiveness and efficiency of the disinfection process.
It is known in the art to monitor the ultraviolet radiation level by deploying one or more passive sensor devices near the operating lamps in specific locations and orientations which are remote from the operating lamps. These passive sensor devices may be photodiodes, photoresistors or other devices that respond to the impingent of the particular radiation wavelength or range of radiation wavelengths of interest by producing a repeatable signal level (e.g., in volts or amperes) on output leads.
In most commercial ultraviolet water disinfection systems, the single largest operating cost relates to the cost of electricity to power the ultraviolet radiation lamps. In a case where the transmittance of the fluid varies from time to time, it would be very desirable to have a convenient means by which fluid transmittance could be measured for the fluid being treated by the system (or the fluid being otherwise investigated) at a given time. If it is found that fluid transmittance is relatively high, it might be possible to reduce power consumption in the lamps by reducing the output thereof. In this way, the significant savings in power costs would be possible.
The measurement of fluid transmittance is desirable since measurement of intensity alone is not sufficient to characterize the entire radiation fieldxe2x80x94i.e., it is not possible to separate the linear effects of lamp aging and fouling from exponential effects of transmittance. Further, dose delivery is a function of the entire radiation field, since not all fluid takes the same path.
The prior art has endeavoured to develop reliable radiation (particularly UV) transmittance measuring devices.
For example, it is known to use a single measurement approach. Unfortunately, the single measurement distance requires re-calibration with fluid of known transmittance to account for fouling.
It is also known to use a two-sensor system in which a first sensor is disposed in air and a second sensor is disposed in water. The problem with this approach is that it results in different fouling of each sensor with resulting errors.
Further, some systems require obtaining a sample from a channel of flowing fluid and thereafter measuring the radiation transmittance of the sample. Unfortunately, this approach necessitates the use of additional fluid handling measures which can lead to non-representative samples.
Thus, despite the advances made in the art, there exists a need for an improved device which can measure radiation transmittance of a fluid. Ideally, the device would have one or more of the following characteristics: it would be of simple construction, it would be submersible, it would require only a single sensor and it could be implemented to measure UV transmittance of a fluid in an on-line or random measurement manner.
It is an object of the present invention to provide a novel optical sensor device which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art.
It is another object of the present invention to provide a novel radiation source module which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art.
It is another object of the present invention to provide a novel process for measuring the transmittance of a fluid in a radiation field.
Accordingly, in one of its aspects, the present invention provides an optical radiation sensor device for detecting radiation in a radiation field having a thickness, the device comprising:
a radiation source;
a radiation sensor element positioned to receive radiation from the radiation source; and
motive means to alter the thickness of the radiation field from a first thickness to a second thickness;
the sensor element capable of detecting and responding to incident radiation from radiation source at the first thickness and at the second thickness.
In another of its aspects, the present invention provides a process for measuring transmittance of a fluid in a radiation field, the process comprising the steps of:
(i) positioning a radiation source and a radiation sensor element in a spaced relationship to define a first thickness of fluid in the radiation field;
(ii) detecting a first radiation intensity corresponding to radiation received by the sensor element at the first thickness;
(iii) altering the first thickness to define a second thickness;
(iv) detecting a second radiation intensity corresponding to radiation received by the sensor element at the second thickness; and
(v) calculating radiation transmittance of the fluid in the radiation field from the first radiation intensity and the second radiation intensity.
In another of its aspects, the present invention provides an optical radiation sensor device for detecting radiation in a radiation field generated in a fluid of interest, the device comprising:
a radiation source submersible in the fluid of interest;
a submersible first radiation sensor element positioned in the fluid of interest at a first distance from the radiation source; and
a submersible second radiation sensor element positioned in the fluid of interest at a second distance from the radiation source;
wherein: (i) the first distance is different from the second distance, (ii) the first radiation sensor element is capable of detecting and responding to incident radiation from radiation source at the first distance, and (iii) the second radiation sensor element is capable of detecting and responding to incident radiation from radiation source at the second distance.
Thus, the present inventors have discovered a novel optical sensor device which, in a preferred embodiment is simplified in construction in that it only requires a single lamp and single sensor element. The sensor element and radiation source (preferably an ultraviolet radiation lamp) are arranged to create a fluid layer therebetween. By altering the thickness of the fluid layer, it is possible to take multiple (i.e., two or more) radiation intensity readings at multiple, known fluid layer thicknesses. Once these are achieved, using conventional calculations, it is possible to readily calculate the radiation transmittance of the fluid. A process for measuring transmittance of a fluid is also described for implementation of the present optical radiation sensor device. Other advantages will become apparent to those of skill in the art.